High resistivity silicon structure and a process for the preparation thereof

ABSTRACT

The present invention generally relates to a high resistivity CZ silicon wafer, or a high resistivity silicon structure derived therefrom, and a process for the preparation thereof. In particular, the high resistivity silicon structure comprises a large diameter CZ silicon wafer as the substrate thereof, wherein the resistivity of the substrate wafer is decoupled from the concentration of acceptor atoms (e.g., boron) therein, the resistivity of the substrate being substantially greater than the resistivity as calculated based on the concentration of said acceptor atoms therein.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application60/682,691, filed May 19, 2005, which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention generally relates to a high resistivity CZ siliconstructure, and a process for the preparation thereof. In particular, thehigh resistivity silicon structure comprises a large diameter CZ siliconwafer, or a substrate derived therefrom, wherein the resistivity of thewafer or substrate is decoupled from the concentration of acceptor atoms(e.g., boron) therein, the resistivity of the structure beingsubstantially greater than the resistivity as calculated based on theconcentration of said acceptor atoms therein. Such a wafer isparticularly well-suited for use in, for example, high frequency (e.g.,microwave or RF) applications.

Traditionally, gallium arsenide (GaAs) wafers have been mostly used inhigh resistivity devices. Gallium arsenide not only has the advantage ofa naturally high carrier mobility, but it also offers the possibility ofhigh resistivity substrates which are required for device isolation andminimization of substrate cross-talk, transmission line loss and makinghigh-Q inductors in radio frequency applications and monolithiccircuits.

Recently, however, as advances in the manufacturing technology for thepreparation of high resistivity single crystal silicon wafers have beenachieved, the use of such wafers in the high resistivity electronicsindustry has expanded. Two methods are used to manufacture singlecrystal silicon: the Czochralski (CZ) method and the floating zone (FZ)method. Although FZ silicon is commercially available havingresistivities of up to about 10 kohm-cm or more, this material haslimitations. For example, such material is expensive to manufacture, itlacks the mechanical stability needed for many applications, at least inpart due to the low oxygen content therein, and it is of limited size.For example, it is not available in diameters of 300 mm or more, whichis the developing industry standard.

Although CZ silicon addresses many of the limitations associated with FZsilicon, CZ silicon prepared by current techniques is also not withoutlimitations. For example, boron is a common contaminant in CZ silicon.In order to grow CZ material of sufficiently high purity to achieve suchhigh resistivities directly, boron concentrations may typically notexceed 1.3×10¹³ atoms/cm⁻³. Manufacturing CZ silicon in commercialenvironments to this level of purity, or beyond, is difficult andexpensive. For example, typically fully synthetic crucibles are needed.However, once such a low boron concentration is achieved, a secondchallenge exists, that being the presence of thermal donors. Thermaldonors are produced during the thermal treatments employed as part ofthe integrated circuit manufacturing process, as a result of thepresence of interstitial oxygen in the CZ silicon.

The formation of thermal donors is generally not problematic in lowresistivity wafers because the residence time in the greater than 300and less than 500 C temperature range within which they typically form,is relatively short, typically about one to two hours, and the majoritycarriers, introduced in n-type or p-type doping, will normally dominate.For high resistivity applications, where the added dopant concentrationis low, however, the formation of thermal donors in the deviceprocessing steps is a major factor in final wafer resistivity. (See,e.g., W. Kaiser et al, Phys. Rev., 105, 1751, (1957), W. Kaiser et al,Phys. Rev., 112, 1546, (1958), Londos et al., Appl. Phys. Lett., 62,1525, 1993.) Thus, for high resistivity CZ applications, residualinterstitial oxygen concentration will strongly influence the rate ofthermal donor formation during device processing.

To-date, solutions proposed to the CZ thermal donor problem haveessentially involved the same approach; that is, these approachesattempt to suppress the oxygen content in the silicon substrate farbelow that which is achievable by the CZ process alone. The idea here isthat for every target value of initial substrate resistivity, there isan oxygen concentration sufficiently low, such that thermal donorgeneration will not be an issue. Typically, this approach involvesthermal treatments to precipitate out of the solid solution the grown-ininterstitial oxygen. However, this approach is costly and timeconsuming, involving long periods of time, typically tens of hours, athigh temperatures.

SUMMARY OF THE INVENTION

Briefly, therefore, the present invention is directed to a highresistivity CZ single crystal silicon wafer. The wafer has a nominaldiameter of at least 150 mm and comprising a concentration of thermaldonors [TD] and acceptors [A], wherein the ratio [TD]:[A] is betweenabout 0.8:1 and about 1.2:1.

The present invention is further directed to a high resistivity siliconstructure comprising a CZ single crystal silicon substrate, thesubstrate having a concentration of thermal donors [TD] and acceptors[A] wherein the ratio [TD]:[A] is between about 0.8:1 and about 1.2:1.

The present invention is still further directed to a high resistivitysilicon structure having a CZ single crystal silicon substratecontaining boron and having a resistivity that is substantially greaterthan the resistivity as calculated based on said boron concentration. Inone preferred embodiment, the resistivity is at least about 5 or about10 times greater than the resistivity as calculated based on the boronconcentration.

The present invention is still further directed to a high resistivity CZsingle crystal silicon wafer, said wafer having a nominal diameter of atleast about 150 mm, containing boron, and having a resistivity that issubstantially greater than the resistivity as calculated based on saidboron concentration. In one preferred embodiment, the resistivity is atleast about 5 or about 10 times greater than the resistivity ascalculated based on the boron concentration.

The present invention is still further directed to a process for thepreparation of one or more of the above-referenced high resistivitysilicon wafers or structures. For example, the present invention isstill further directed to a process for preparing a high resistivitysilicon structure, the process comprising subjecting a siliconstructure, which comprises a CZ single crystal silicon substrate havingan initial resistivity of at least about 50 ohm-cm, to a heat-treatmentfor a duration and at a temperature such that the resulting substrate ofthe heat-treated structure has a concentration of thermal donors [TD]and acceptors [A] wherein the ratio [TD]:[A] is between about 0.8:1 andabout 1.2:1.

The present invention is still further directed to a process forpreparing a high resistivity CZ single crystal silicon wafer, theprocess comprising subjecting a CZ single crystal silicon wafer having anominal diameter of at least 150 mm and an initial resistivity of atleast about 50 ohm-cm to a heat-treatment for a duration and at atemperature such that the resulting heat-treated wafer has aconcentration of thermal donors [TD] and acceptors [A] wherein the ratio[TD]:[A] is between about 0.8:1 and about 1.2:1.

The present invention is still further directed to a process forpreparing a high resistivity silicon structure. The process comprisessubjecting a silicon structure, which comprises a CZ single crystalsilicon substrate containing boron and interstitial oxygen and having aninitial resistivity of at least about 50 ohm-cm, to a heat-treatment fora time and at a temperature sufficient to obtain a single crystalsilicon structure having a CZ single crystal silicon substrate with aresulting resistivity that is substantially greater than the resistivityas calculated based on the boron concentration therein. In one preferredembodiment, the resistivity is at least about 5 or about 10 timesgreater than the resistivity as calculated based on the boronconcentration.

The present invention is further directed to a process for preparing ahigh resistivity CZ single crystal silicon wafer. The process comprisessubjecting a CZ single crystal silicon wafer containing boron andinterstitial oxygen and having an initial resistivity of at least about50 ohm-cm to a heat-treatment for a time and at a temperature sufficientto obtain a CZ single crystal silicon wafer with a resulting resistivitythat is substantially greater than the resistivity as calculated basedon the boron concentration therein. In one preferred embodiment, theresistivity is at least about 5 or about 10 times greater than theresistivity as calculated based on the boron concentration.

The present invention is still further directed to one of the precedingprocesses wherein the boron concentration [B] and the oxygenconcentration [Oi] of the substrate of the structure, or wafer, and thetemperature, T, of the heat-treatment, are related by the followingequation:[B]=1e14([O _(i) ]/[O _(i)]_(ref))^(n)exp(E/kT−E/kT _(ref))wherein: [B] is the boron concentration; [Oi]_(ref) is the referenceinterstitial oxygen concentration and is about 6.6e17 cm⁻³; [Oi] is theactual interstitial oxygen concentration of the wafer or substrate ofthe structure; n is the oxygen exponent and is about 7; E is theactivation energy and is about 4 eV; k is the Boltzmann constant; T isthe actual temperature of the heat-treatment; and, T_(ref) is thereference temperature and is about 520° C., and further wherein: (i) fora given boron concentration, [B], the oxygen concentration may be about+/−0.5 ppma of the calculated concentration and the temperature of theheat-treatment may be about +/−10° C. of the calculated temperature;(ii) for a given oxygen concentration, [Oi], the boron concentration maybe about +/−20% of the calculated concentration and the temperature ofthe heat-treatment may be about +/−10° C. of the calculated temperature;and, (iii) for a given temperature of the heat-treatment, T, the oxygenconcentration may be about +/−0.5 ppma of the calculated concentrationand the boron concentration may be about +/−20% of the calculatedconcentration.

The present invention is still further directed to an assembly of thepreceding silicon structures and/or wafers, said assembly comprising forexample at least about 10, 20 or more of the structures or wafers.

The present invention is still further directed to one of the precedingsilicon wafers, wherein said wafer has an epitaxial silicon layerdeposited on a surface thereof. Alternatively, the present invention isdirected to a silicon-on-insulator structure comprising one of thepreceding silicon wafers, wherein said wafer serves as the substrate, orhandle wafer, of said silicon-on-insulator structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphical illustration of the generally accepted view of howthermal donor concentration changes in CZ single crystal silicon overtime, when annealed at a temperature of about 450° C. or less. It is tobe noted that the slope of the line illustrated herein is generallyunderstood to be dependent upon the oxygen concentration, to the fourthpower, in the silicon being annealed.

FIG. 2 is a graphical illustration of the initial formation rates ofthermal donors.

FIG. 3 is a graphical illustration of the typical behavior ofresistivity during the generation of thermal donors (TDs) duringannealing. This is a calculated example using a typical TD generationrate of about 1e14 cm⁻³/hour and an initial 100 ohm-cm p-type(approximate) sample. In this graph, negative resistivity valuesindicate n-type conductivity.

FIG. 4 is a graphical illustration of the effect of starting resistivityonly on TD influenced resistivity during anneals. This is a calculatedexample using a typical TD generation rate of about 1e14 cm⁻³/hour andinitial resistivities of about 80, 100 and 120 ohm-cm (p-type). In thisgraph, negative resistivity values indicate n-type conductivity.

FIG. 5 is a graphical illustration of the effect of oxygen concentrationrange on TD influenced resistivity during anneals. These are calculatedexamples using a typical TD generation rate of about 1e14 cm⁻³/hour forthe middle of a hypothetical oxygen concentration range. For a typicaloxygen concentration dependence of about [Oi]⁴, the rate range spannedin this graphical illustration would correspond to an oxygenconcentration range of about +/−0.5 ppma. The initial resistivity of allexamples herein is 100 ohm-cm p-type. In this figure, negativeresistivity values indicate n-type conductivity.

FIG. 6 is a graphical illustration of how, in accordance with thediscovery of present invention, thermal donor concentration changes inCZ single crystal silicon over time, when annealed at temperatures inexcess of those conventionally applied (e.g., about 480° C. or more). Itis to be noted that, in accordance with the present invention, it hasbeen discovered that, at elevated temperatures, the concentration ofthermal donors reaches a plateau for a period of time.

FIGS. 7 a and 7 b are graphical illustrations of kinetic curves for TDgeneration (curve 1) and for decay of pre-generated TDs (curve 2), forannealing at about 560° C. (FIG. 7 a) and at about 570° C. (FIG. 7 b).

FIG. 8 is a graphical illustration of the measured, saturated, addedelectron concentration in low boron concentration material (about 2e12cm⁻³) for two different oxygen concentrations, as a function oftemperature. The lower curve (squares) is for a lower oxygenconcentration.

FIGS. 9 a and 9 b are graphical illustrations of the loci of points intemperature, initial resistivity and oxygen concentration space in whichthe conditions for achieving the high resistivity state by the presentinvention are met (as defined by Equation (1a)). In FIG. 9 a, thenumbers 1-4 on the curves refer to oxygen concentrations of (5, 6, 7 and8)×10¹⁷ cm⁻³, respectively (these concentrations correspond to 10, 12,14 and 16 ppma, respectively).

FIGS. 10 a to 10 d are 4 plots which illustrate “spreading resistance”measurement data taken on one wafer subjected to the process of thepresent invention, in order to raise the resistivity, wherein uniformityof the effect achieved by the present process is illustrated therein.The resistivity, as a function of depth in the wafer, was measured atfour different points along the radius. The radial positions are givenas 1, 3, 5 and 7 cm from the edge of a 200 mm wafer, respectively (i.e.,FIG. 10 a is 1 cm from the edge, FIG. 10 b is 3 cm from the edge, FIG.10 c is 5 cm from the edge, and FIG. 10 d is 7 cm from the edge). Eachcurve is the resistivity from the front surface “0” toward the back. Thescales run from 0 to 600 microns. The total thickness of the wafers wasabout 675 microns. The measured data closely follows the value 10³ atessentially all radial positions at essentially all depths. This datashows that the present process is capable of delivering substantiallyuniform results in both radius and depth. (In these graphs, the Y axisis resistivity, the range thereon being from 10⁻² ohm-cm up to 10⁵ohm-cm; that is, from bottom to top, the horizontal lines denote aresistivity of 10⁻², 10⁻¹, 10⁰, 10¹, 10², 10³, 10⁴, and 10⁵ ohm-cm,respectively. The X axis is the depth, the range thereon being 0 to 600microns; that is, each vertical line on the X axis denotes an incrementof 50 microns, from 0 to 600 microns.)

FIG. 11 is a graphical illustration which shows a calculated example inwhich, applying an [Oi]⁴ dependence, the oxygen concentration of thepopulation varies by only about +/−0.1 ppma (thermal donor rate approx.100 ohm-cm).

FIG. 12 is a flow chart or block diagram which illustrates an embodimentof the present invention, wherein the thermal treatment detailed hereinis performed after a metalization step in the device manufacturingprocess.

FIG. 13 is a flow chart or block diagram which illustrates analternative embodiment of the present invention, wherein the thermaltreatment detailed herein is performed before a metalization step in thedevice manufacturing process.

FIG. 14 is a graphical illustration of the creation of a highresistivity state using the approximate annealing temperature derivedfrom FIGS. 9 a and 9 b, knowing the approximate sample [B] and [Oi]. Thesolid dots refer to n-type conductivity. The open dots refer to p-typeconductivity.

FIG. 15 is a graphical illustration of saturated resistivity valuesobtained with samples similar to those used for the results of FIG. 14,but varying the temperature around the central or “ideal” value (forthis particular example) of about 530° C. A broad window in theacceptable anneal temperature is observed.

FIGS. 16 a and 16 b are graphical illustrations of calculatedresistivities for excursions or variations from the “ideal” temperaturefor compensation within a simple model involving only “normal” thermaldonors and no “reconstructing” thermal donors. FIG. 16 a illustratesresistivity for boron concentration of about 2e¹³ cm⁻³ (curve 1) andabout 2e¹⁴ cm⁻³ (curve 2). FIG. 16 b illustrates the resistivityenhancement factor, which is universal for essentially any initialresistivity.

FIG. 17 is a graphical illustration of the effect of a 400° C. anneal onthe resistivity of high-resistivity samples. The open symbols correspondto p-type, while the filled symbols correspond to n-type.

FIG. 18 a to 18 d are graphical illustrations of the high resistivitystates obtained in thermally treated samples having a large [Oi] denudedzone. More specifically, 18 a illustrate the results of a treatment at530° C. only, applied after an 1100° C. outdiffusion anneal. FIG. 18 billustrates the results of a treatment at 530° C., applied after an1100° C. outdiffusion anneal and then a pre-anneal at 450° C. (i.e., anormal thermal donor create anneal at 450° C. was performed prior to theanneal at 530° C. and after the anneal at 1100° C.). FIG. 18 cillustrates the results of a treatment at 530° C., applied with nooutdiffusion anneal and no pre-anneal to form thermal donors. FIG. 18 dillustrates the results of a treatment at 530° C., performed after apre-anneal at 450° C. to form thermal donors. In all figures here, depthdependent (0 to 120 microns) of resistivity (SRP) is shown.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with the present invention, and as set forth in greaterdetail herein below, it has been discovered that a CZ single crystalsilicon wafer, or a silicon structure comprising a substrate derivedfrom such a wafer, may be prepared in accordance with the process of thepresent invention to have a resistivity which essentially becomesdecoupled from the concentration of acceptor atoms (e.g., boron atoms)therein. The present process employs a controlled thermal treatment ofthe silicon wafer, or silicon structure comprising a substrate derivedfrom such a wafer, in order to form thermal donors therein, which act to“cancel out” the effect acceptors atoms present therein have on theresistivity thereof. As a result, a CZ single crystal silicon wafer, ora silicon structure comprising a substrate derived from such a wafer,may be prepared to have a very high resistivity (e.g., a resistivity,for example, in the range of thousands to tens of thousands of ohm-cm).

1. Compensation or “Cancelling Out”

With respect to resistivity, the general concept of “compensation”between acceptor atoms (e.g., boron atoms) and donor atoms (e.g., oxygenclusters, known as thermal donors because they are formed upon heatingto elevated temperature), is known and relates to the idea of cancellingout the effect acceptor atoms, such as boron atoms, have on theresistivity of silicon by adding, or introducing, donor atoms, such asoxygen thermal donors, to the silicon. Although this concept is known,to-date it has not been applied in a way which achieves compensationover a substantial portion of a large diameter CZ silicon wafer (e.g., anominal diameter of greater than 150 mm, 200 mm, 300 mm or more), or asubstrate derived therefrom. In general, and without being held to aparticular theory, it is believed that failed attempts to achieve such aresult to-date are due to the belief that compensation may be achievedonly when four variables are matched: (i) thermal donor atomconcentration, (ii) acceptor atom concentration, (iii) duration of thethermal treatment employed to form the thermal donors, and (iv)temperature of that thermal treatment.

a. Thermal Donor Effect on Resistivity: Thermal Treatments Below 450° C.

Referring now to FIG. 1, currently, the generally accepted view is thatthermal donor concentration, [TD], increases as the duration of heatingincreases, the rate of increase (i.e., the slope of the line in FIG. 1)being dependent, to the fourth power, on the oxygen concentration in theCZ silicon being heated. However, this view is essentially based onthermal treatments performed at a temperature of about 450° C. or less.

The added electrons due to the generation of thermal donors maymeasurably affect the resistivity, and type, of a piece of silicon.However, this is generally only true if the concentration of theresulting additional electrons (2× the concentration of the TDsthemselves) approaches the concentration (e.g., within about a fewpercent, such as less than about 5%, 4%, 3%, 2% or less) of the dopantconcentration, or exceeds it. The rate at which TDs are created dependsprimarily on two things: 1) the temperature of the anneal; and, 2) theoxygen concentration. Referring now to FIG. 2, the result of arelatively recent study of the rate of TD formation as a function ofthese two variables is illustrated. (See, e.g., Landos et al., Appl.Phys. Lett., 62, 1525 (1993).)

In p-type silicon, when the total concentration of TD generatedelectrons begins to get close to the concentration of the dopant(usually boron), resistivity rapidly increases, as the boron generatedholes are being “compensated” by the TD generated electrons, steadilytoward an extremely high value (e.g., perhaps as high as about 300kohm-cm), at the point where the TD electron concentration about equalsthe boron concentration. As the TD electron concentration increasesfurther beyond that of the boron concentration, the majority carrierbecomes electrons and the type of the material is converted from p-typeto n-type. As yet more TD electrons are created, the resistivity beginsto rapidly decrease while remaining n-type. An example of typicalresistivity behavior during TD generation is shown in FIG. 3. This is acalculated case assuming a typical TD generation rate of 1e14 cm⁻³/hrand an initially 100 ohm-cm p-type sample.

A very high resistivity state is achieved for only a very short periodof time (typically on the order of minutes, for example less than about30 minutes, 20 minutes, 10 minutes or even 5 minutes) at some pointduring the anneal. The position in time during annealing of thisextremely high resistivity state and the changeover from p-type ton-type depends on the rate of TD generation, and hence on theconcentration of oxygen and the temperature of the anneal, and on theconcentration of boron in the sample being annealed.

Since the peak of the resistivity versus time graphs depend on amatching of the generated TDs to the boron concentration, the shape ofthe curves depend on the initial resistivity of the sample, even ifeverything else (e.g., anneal temperature and oxygen concentration) isessentially the same. FIG. 4 illustrates this point, wherein thedevelopment of resistivities of three samples is calculated. From this,it can be seen that the resulting resistivities of the materials (havingstarting resistivities of about 80, 100 and 120 ohm-cm) are close, butnot equal.

The oxygen concentration dependence of TD formation rates is large. At aTD formation temperature of about 500° C., it is found to be [Oi]⁹,while at about 450° C. it is [Oi]⁴, and at about 400° C. it is about[Oi]². To see the effect of such a dependence, we may consider thefollowing example. A typical oxygen concentration specification is +/−1ppma. Using the example of the least strong dependence on [Oi]:[Oi]², wemay compare the effect of a change in generation rate of +/−0.25e14around our typical example rate of 1e14 cm⁻³/hour. This is illustratedin FIG. 5. More realistically, for the more typical TD generationtemperature 450° C. (and corresponding to a rate dependence of [Oi]⁴),the same variation in the rate dependence would correspond to asignificantly tighter oxygen concentration range (i.e., +/−0.5 ppmaaround a target value).

b. Thermal Donor Effect on Resistivity: Thermal Treatments Above 450° C.

In contrast, and referring now to FIG. 6, it has been discovered, inaccordance with the present invention, that if the CZ silicon is heatedto higher temperatures (e.g., greater than about 480° C., about 490° C.,about 500° C. or more, such as between about 480° C. and about 600° C.,or between about 485° C. or about 490° C. and about 590° C., or betweenabout 500° C. and about 575° C., as detailed elsewhere herein), theconcentration of thermal donors increases, but not monotonically, as inthe case with conventional thermal donors (e.g., up to some maximum ofabout 1e16 cm⁻³). Rather, at some point this concentration saturates, orreaches a plateau, for a period of time (e.g., at least about 30minutes, about 60 minutes, about 90 minutes, about 120 minutes or more).Stated another way, the thermal donor concentration may increaseinitially, but at some point during this heat treatment the rate atwhich the thermal donor concentration is increasing is substantiallyreduced, and may become substantially constant (see, e.g., FIGS. 7 a, 7b and 8), for a period of time. If the heat treatment continues for asufficiently long period of time, the thermal donor concentration mayonce again begin to increase.

The value of the added electron concentration of the plateau region wasfound to be dependent on the anneal temperature and the oxygenconcentration of the samples. The same plateau region in added electronconcentration is reached regardless of whether the sample hadpre-generated thermal donors (from a prior TD anneal at, say 450° C.) ornot. Two examples of plateau regions found in samples of oxygenconcentration of 6e17 cm-3 (initially about 300 ohm-cm p-type borondoped) are shown in FIGS. 7 a and 7 b for annealing temperatures of 560°C. and 570° C., respectively.

As illustrated by the equation below, the concentration of addedelectrons, N, in the plateau region was found to exhibit an Arrheniusrelationship with temperature, wherein E equals about 4.2 eV. The oxygenconcentration dependence is estimated to be in a power law relation,with n equal to about 7.N˜[Oi] ⁷exp[4.2 eV/kT]FIG. 8 shows annealing temperature and oxygen concentration data for theplateau, or saturated, added electron concentrations experimentallydetermined to-dated.

Having a relatively wide plateau of saturated electron concentration intime is useful for a viable process of increasing the resistivity of apopulation of silicon wafers. It would be some improvement over theconventional thermal donor approach to match the added electronconcentration of the plateau region with the background boronconcentration. The system would not be as sensitive to the annealingtime. However, this is typically not enough for a satisfactorycommercial solution, because it reduces the restrictions on only one ofthe four variables, that being time. The restrictions on the other threevariables (i.e., [Oi], [B], and anneal temperature), remain.

Conventional knowledge in the art suggests that, even if the above-notedwindow of time exists, wherein thermal donor concentration saturates orplateaus, thermal donor concentration must still be in preciserelationship with the acceptor concentration (e.g., one-half of thethermal donor concentration is equal to the boron concentration), inorder to achieve a high resistivity state in the CZ silicon. However, inaccordance with the present invention, it has been further discoveredthat this is not the case; that is, there does not have to be a precisematch between the value of the acceptor atom concentration (e.g., boronatom concentration) and the saturated or plateau electron concentration(which is a function of the thermal donor concentration), by means offor example controlling the anneal temperature and time. Rather, simplygetting these two close to one another is sufficient. Without being heldto a particular theory, it is generally believed that this is the casebecause the high resistivity state is the natural state of this system,and thus the system simply adjusts itself to the high resistivity statewhen these two are close enough to each other. As a result, there is acommercially practical window of operation here.

Additionally, and also without being held to any particular theory, itis further believed that a key point here is the controlled creation, inthe higher reaches of the thermal donor temperature range (e.g., Tgreater than about 480° C.) of a second type of thermal donor, distinctfrom the “normal” thermal donor. This new type of thermal donor may becharacterized as a “reconstructing” species and one that allows for thesystem to “self-compensate” to adjust itself to a high resistivitystate. In contrast, the “normal” type is a “stable” type. Accordingly,what is preferably to be done to create a high resistivity state by thisapproach is as follows—one approximately matches the plateauconcentration for a given oxygen concentration and temperature to theboron concentration one wishes to compensate. To this end, the data ofFIG. 8, and from it an analytical expression for this (i.e., Equation(1a) set forth below), may be used to roughly estimate the allowablecombinations of oxygen concentration and anneal temperature to produce asaturated excess electron concentration somewhere close (as furtherdetailed herein below) to the boron concentration. Alternatively, byfixing any one of the three variables, [Oi], [B], or T, and the possiblecombinations of the other two may be worked out. Fixing two of the threevariables thus fixes the third.

2. High Resistivity Silicon and Process for the Preparation Thereof

a. Thermal Treatment

In view of the foregoing, it is to be noted that, in accordance with thepresent invention, a CZ single crystal silicon wafer, or a siliconstructure comprising a substrate derived from such a wafer, comprisingacceptor atoms, in particular boron, and interstitial oxygen, may besubjected to a thermal treatment for a time and at a temperaturesufficient to yield a wafer, or silicon structure comprising a substratederived from such a wafer, which has a resistivity that is substantiallygreater than the resistivity as calculated based on the concentration ofacceptor atoms (e.g., boron) therein. As such, the resulting wafer, orsubstrate of the silicon structure, has a resistivity that isessentially “decoupled” from the concentration of acceptor atoms (e.g.,boron) therein.

It is to be noted that, as used herein, the resistivity of the resultingheat treated CZ single crystal silicon wafer, or the resulting heattreated CZ single crystal silicon substrate of the resulting siliconstructure, is “substantially greater than” the resistivity as calculatedbased on the concentration of acceptor atoms (e.g., boron) therein, whenthe resistivity is at least about 5 times greater than the calculatedresistivity, and preferably is at least about 10 times, still morepreferably about 15 times, still more preferably about 20 times, stillmore preferably about 25 times, still more preferably about 30 times,still more preferably about 35 times, still more preferably about 40times, still more preferably about 45 times, still more preferably about50 times, still more preferably about 55 times, still more preferablyabout 60 times, still more preferably about 65 times, still morepreferably about 70 times, still more preferably about 75 times, stillmore preferably about 80 times, still more preferably about 85 times,still more preferably about 90 times, still more preferably about 95times, and still more preferably about 100 times greater than thecalculated resistivity.

In accordance with the present invention, and as further detailed hereinbelow, it has been discovered that such a wafer, or silicon structure,may be obtained when the relationship between acceptor concentration(e.g., boron concentration [B]), interstitial oxygen concentration [Oi],and temperature, T, of the heat-treatment is sufficiently controlled,such that the detrimental effects of acceptors and thermal donors onresistivity are significantly reduced. In particular, it has beendiscovered that, for example, the boron concentration, [B], interstitialoxygen concentration, [Oi], and temperature, T, of the heat-treatmentmay be related by the following Equation (1a):[B]=1e14([O _(i) ]/[O _(i)]_(ref))^(n)exp(E/kT−E/kT _(ref))  (1a)wherein:

-   -   [B] is the boron concentration;    -   [Oi]_(ref) is the reference interstitial oxygen concentration        and is about 6.6e17 cm^(−3;)    -   [Oi] is the actual interstitial oxygen concentration of the        wafer or substrate;    -   n is the oxygen exponent and is about 7;    -   E is the activation energy and is about 4 eV;    -   k is the Boltzmann constant;    -   T is the actual temperature of the heat-treatment; and;    -   T_(ref) is the reference temperature and is about 520° C.;        and further wherein, in view of flexibility afforded by the        present invention, and in accordance with the relationships set        forth above in Equation (1a):    -   (i) for a given boron concentration, [B], the oxygen        concentration may be about +/−0.5 ppma, preferably about +/−0.4        ppma, more preferably about +/−0.3 ppma, and still more        preferably about +/−0.25 ppma of the calculated concentration        and the temperature of the heat-treatment may be about +/−10°        C., preferably about +/−9° C., more preferably about +/−8° C.,        still more preferably about +/−6° C., and still more preferably        about +/−5° C. of the calculated temperature;    -   (ii) for a given oxygen concentration, [Oi], the boron        concentration may be about +/−20%, preferably about +/−18%, more        preferably about +/−16%, still more preferably about +/−14%,        still more preferably about +/−12%, and still more preferably        +/−10% of the calculated concentration and the temperature of        the heat-treatment may be about +/−10° C., preferably about        +/−9° C., more preferably about +/−8° C., still more preferably        about +/−6° C., and still more preferably about +/−5° C. of the        calculated temperature; and/or,    -   (iii) for a given temperature of the heat-treatment, T, the        oxygen concentration may be about +/−0.5 ppma, preferably about        +/−0.4 ppma, more preferably about +/−0.3 ppma, and still more        preferably about +/−0.25 ppma of the calculated concentration        and the boron concentration may be about +/−20%, preferably        about +/−18%, more preferably about +/−16%, still more        preferably about +/−14%, still more preferably about +/−12%, and        still more preferably +/−10% of the calculated concentration.        In this regard it is to be understood that any number recited        above for boron concentration, as it relates to oxygen        concentration and/or the heat-treatment temperature, may be used        in combination with any number recited above for oxygen        concentration, and vice versa. Additionally, it is to be        understood that any two numbers recited above for boron        concentration (or oxygen concentration) may be used in        combination to define a range of acceptable concentrations for        boron (or oxygen), in accordance with the present invention.

Referring now to FIG. 9, some representative plots of calculationsperformed using Equation (1a) are provided for purposes of illustration.Additionally, Examples provided herein below (e.g., Examples 1-3)further illustrate results that may be obtained using the above-notedequation, and the methods detailed herein.

With respect to Equation (1a), it is to be noted that, in practice, thecombination of the parameters may be freely chosen, or one or two of theparameters may be fixed by some other consideration (e.g., the annealtemperature, for example, may be limited by requirements of theintegrated circuit manufacturing process). Additionally, fixing two ofthe parameters acts to restrict the choice of the third.

Also with respect to Equation (1a), it is to be noted that afterchoosing a set of suitable process parameters, a sample may be annealedat the required temperature for a period of time. This required time isgenerally on the order of, for example, about 30 to about 120 minutes,but may be longer (e.g., about 150 to about 250 minutes) or shorter(e.g., about 10 to about 25 minutes). The actual time required forannealing the sample may vary and may require some generalexperimentation to determine. Following the annealing, the sample is ina highly resistive state.

It is to be still further noted that Equation (1a) may optionally beexpressed more generally in terms of acceptor concentration, rather thanboron concentration. However, experience to-date indicates that boron isthe most common acceptor, and thus typically of most concerned, in CZsingle crystal silicon. As such, reference will typically be made toboron concentration throughout the present document. However, it is tobe understood that such references may optionally be more generallyinterpreted to reference acceptor concentration.

It is to be still further noted that, based on experience to-date and asset forth in greater detail elsewhere herein, the temperature for whichthe above-noted relationship is optimal is typically within the range ofat least about 480° C. to less than about 600° C., or at least about485° C. or about 490° C. to less than about 580° C., or at least about500° C. and about 575° C. Durations for the heat-treatment may alsovary, as detailed elsewhere herein, but typically are within the rangeof at least about 10 minutes to less than about 250 minutes, or about 15to about 200 minutes, or about 20 to about 150 minutes.

In view of the foregoing, the present invention accordingly enables thepreparation of a CZ single crystal silicon wafer, or a silicon structurecomprising a substrate derived from such a wafer, wherein theconcentration of thermal donors [TD] and acceptors [A] are such that theratio, [TD]:[A], of the two is between about 0.8:1 and about 1.2:1, andoptionally is between about 0.85:1 and 1.15:1, between about 0.9:1 and1.1:1, or between about 0.95:1 and 1.05:1. For example, this ratio maybe about 0.8:1, about 0.85:1, about 0.9:1, about 0.95:1, about 1:1,about 1.05:1, about 1.1:1, about 1.15:1, or about 1.2:1. In oneparticular embodiment, however, the ratio is something other than 1:1.

Referring now to FIGS. 10 a to 10 d, it is to be noted that the processof the present invention preferably enables a resistivity (i.e., theration [TD]:[A], or a resistivity value as recited elsewhere herein) tobe achieved in the heat treated CZ wafer, or substrate derived from a CZwafer, throughout substantially all of the wafer or substrate (i.e., atleast about 80%, 85%, 90%, 95% or even 100% of the CZ silicon wafer orsubstrate may be effectively converted to this high resistivity state);alternatively, however, at least about 20%, 30%, 40%, 50%, 60%, or evenabout 70% of the wafer or substrate is converted to this highresistivity state. Additionally, or optionally, a high resistivityregion may be formed in the wafer, or substrate, which extends over atleast about 20%, and preferably at least about 30%, 40%, 50%, 60%, 70%,80%, 90% or even about 95% of the radial surface, and/or has a depth orthickness which is at least about 20%, and preferably at least about30%, 40%, 50%, 60%, 70%, 80%, 90% or even about 95% of the wafer orsubstrate thickness. For example, in one preferred embodiment, the highresistivity region may extend over about 50% to about 95%, or about 70%to about 90%, of the surface of the wafer, or substrate, and preferablyabout 50% to about 95%, or about 70% to about 90%, of the thickness ofthe wafer, or substrate.

In this regard, it is to be understood that, with respect to the portionof the wafer or substrate that may be effectively converted to a highresistivity state by means of the thermal treatment of the presentinvention, any percentages recited above for the surface may be used incombination with any percentage recited above for thickness, and viceversa. Additionally, it is to be understood that any two percentagesrecited above for the surface (or thickness) may be used in combinationto define a range, in accordance with the present invention.

In contrast to conventional methods of producing high resistivity CZsilicon, which focus on ways to minimize the concentration of thermaldonors and acceptors in the single crystal silicon, the presentinvention enables essentially any CZ wafer to be utilized, provided therelationship between the oxygen concentration, boron concentration andheat treatment temperature are properly controlled (i.e., therelationship expressed in Equation (1a) is satisfied/maintainedtherein), and further provided that the temperature of the heattreatment is sufficiently high such that, as further detailed herein,thermal donors will be formed from the interstitial oxygen. Typically,however, the CZ single crystal silicon wafer, or the substrate of thesilicon structure, that is subjected to the present heat treatment mayhave an initial resistivity (and thus boron concentration, as furtherdetailed herein) of at least about 50 ohm-cm, and preferably may have aninitial resistivity of at least about 100 ohm-cm, about 150 ohm-cm,about 200 ohm-cm, about 250 ohm-cm, about 300 ohm-cm or more.Accordingly, this starting wafer, or substrate of the starting siliconstructure, may have an initial resistivity ranging from, for example, atleast about 50 or 100 ohm-cm to less than about 300 ohm-cm, from about125 to about 250 ohm-cm, or from about 150 to about 200 ohm-cm.

In this regard it is to be noted that the initial resistivity of the CZsilicon wafer, or the substrate of the silicon structure, may, in onepreferred embodiment, essentially correspond to the boron concentrationtherein. As such, the above-noted resistivities may alternatively beviewed in terms of boron concentration, the resistivity and boronconcentrations being inversely related (i.e., as the resistivityincreases, the boron concentration decreases). Accordingly, the boronconcentration of the wafer, or substrate of the silicon structure, maytypically be less than about 2.6×10¹⁴ cm⁻³, and may preferably be lessthan about 1.3×10¹⁴ cm⁻³, about 8.7×10¹³ cm⁻³, about 6.5×10¹³ cm⁻³,about 5.2×10¹³ cm⁻³, about 4.3×10¹³ cm⁻³ or less. The starting wafer, orsubstrate of the starting silicon structure, may therefore have a boronconcentration in the range of, for example, about 4.3×10¹³ cm⁻³ to about2.6×10¹⁴ cm⁻³, about 5.2×10¹³ cm⁻³ to about 1.3×10¹⁴ cm⁻³, or about6.5×10¹³ cm⁻³ to about 8.7×10¹³ cm⁻³.

It is to be still further noted that the starting wafer, or startingsilicon structure, may additionally or optionally be limited by theoxygen concentration therein. More specifically, it is to be noted thatthe oxygen concentration of the wafer to be subjected to the presentheat treatment, or substrate of the silicon structure that is to besubjected to the present heat treatment, is typically in the range offrom at least about 5 ppma to less than about 20 ppma, and preferably isin the range of from about 6 ppma to about 18 ppma, from about 8 ppma toabout 16 ppma, from about 10 to about 15 ppma, or even from about 12ppma to about 14 ppma. (See, e.g., FIG. 11, from which it can beobserved that the oxygen concentration required in order to achieve highresistivity increases rapidly as the initial resistivity drops belowabout 20 ohm-cm. FIG. 11 illustrates a calculated example in which,applying an [Oi]⁴ dependence, the oxygen concentration varies only+/−0.1 ppma. Such a variation is within the measurement errors of theFTIR method to determine the oxygen concentration. However, in spite ofthe narrowness of this hypothetical range of oxygen concentration, thereis practically no overlap in annealing times in which a high resistivitystate is achieved.)

As further detailed elsewhere herein, the temperature of the heattreatment to be employed is preferably selected in cooperation with themanufacturing process of the desired silicon structure (e.g., a desiredelectronic or electrical device); that is, the temperature of the heattreatment is preferably a temperature that is employed in the siliconstructure manufacturing process, or is tolerable within themanufacturing process (i.e., may be used in the manufacturing processwithout causing unacceptable changes in the overall process or resultingsilicon structure obtained therefrom). More preferably, the heattreatment step of the present invention will itself be carried out aspart of the actual manufacturing process; that is, a CZ single crystalsilicon wafer to be employed in the manufacture of a silicon structure(e.g., a device) will preferably have a boron concentration and anoxygen concentration that are suitably paired, in accordance with therelationship disclosed herein (see, e.g., Equation (1a), above), suchthat, when subjected to a heat treatment commonly employed in themanufacturing process of a desired silicon structure (e.g., a device),the resulting high resistivity structure of the present invention willbe obtained.

With respect to the temperature of the heat treatment, however, it is tobe noted that, generally speaking, the temperature employed in the heattreatment will typically be greater than about 480° C. and less thanabout 600° C. (e.g., a temperature of less than about 590° C., 580° C.,570° C., 560° C., 550° C., 540° C., 530° C., 520° C., 510° C., 500° C.,or even about 490° C.). As such, the temperature of the heat treatmentmay be in the range of, for example, greater than about 480° C. to lessthan about 600° C., from greater than about 485° C. or 490° C. to lessthan about 580° C., from greater than about 500° C. to less than about575° C., from greater than about 510° C. to less than about 550° C., orfrom greater than about 520° C. to less than about 530° C.

The duration of the heat treatment may vary, as the temperature, boronconcentration and/or oxygen concentration changes. A suitable durationfor a given set of condition (i.e., temperature, boron concentrationand/or oxygen concentration) may be determined experimentally by meanscommon in the art. Typically, however, the duration of the present heattreatment may be greater than about 5 minutes and less than about 250minutes, and preferably less than about 200 minutes, about 150 minutes,about 125 minutes, about 120 minutes, about 110 minutes, about 100minutes, about 90 minutes, about 80 minutes, about 70 minutes, about 60minutes, about 50 minutes, about 40 minutes, about 30 minutes, or evenabout 20 minutes. Accordingly, the wafer, or silicon structure, may besubjected to the present heat treatment for a duration of about 10 toabout 250 minutes, from about 15 to about 200 minutes, from about 20 toabout 150 minutes, from about 25 to about 125 minutes, from about 30 toabout 120 minutes, from about 35 to about 110 minutes, from about 40 toabout 100 minutes, from about 50 to about 90 minutes, or from about 60to about 80 minutes. In this regard it is to be noted that, typically,higher temperatures are employed with shorter durations, and vice versa.

In accordance with the present process, it is to be noted that theresulting heat treated CZ wafer, or CZ substrate of the heat treatedsilicon structure, may have a resistivity after said heat-treatment ofat least about 500 ohm-cm, about 750 ohm-cm, about 1000 ohm-cm, about1500 ohm-cm, about 2000 ohm-cm, about 2500 ohm-cm, about 3000 ohm-cm,about 3500 ohm-cm, about 4000 ohm-cm, about 4500 ohm-cm, about 5000ohm-cm, or more (e.g., about 5500 ohm-cm, about 6000 ohm-cm, about 6500ohm-cm, about 7000 ohm-cm, about 7500 ohm-cm, about 8000 ohm-cm, about8500 ohm-cm, about 9000 ohm-cm, about 9500 ohm-cm, about 10000 ohm-cm,about 20000 ohm-cm, or even about 30000 ohm-cm).

In this regard it is to be noted that this high resistivity may extendacross the diameter or width, and/or thickness, of the wafer orsubstrate. Alternatively, however, a high resistivity region may beformed in the wafer, or substrate, which extends over at least about20%, and preferably at least about 30%, 40%, 50%, 60%, 70%, 80%, 90% oreven about 95% of the radial surface, and/or has a depth or thicknesswhich is at least about 20%, and preferably at least about 30%, 40%,50%, 60%, 70%, 80%, 90% or even about 95% of the wafer or substratethickness. For example, in one preferred embodiment, the highresistivity region may extend over about 50% to about 95%, or about 70%to about 90%, of the surface of the wafer, or substrate, and preferablyabout 50% to about 95%, or about 70% to about 90%, of the thickness ofthe wafer, or substrate.

In this regard it is to be still further understood that any numberrecited above for a given parameter, be it for a particular ratio,concentration, temperature, time, resistivity, etc., may be used incombination with any other number for one or more other parameters notedherein, without departing from the scope of the present invention.Additionally, it is to be understood that any two numbers recited abovefor a given parameter, be it for a particular ratio, concentration,temperature, time, resistivity, etc., may be used in combination todefine a range of ratios, concentrations, temperature, times,resistivities, etc., in accordance with the present invention andwithout departing from the scope thereof.

b. Cooling after Thermal Treatment

Experience to-date suggest that, in at least some instances, the coolconditions (e.g., cooling rate) after the thermal treatment detailedherein above may not be narrowly critical to the present invention. Forexample, some experiments have been made on the effect of cooling ratefollowing annealing a silicon wafer at a temperature suitable forcreating the high resistivity state detailed herein. Comparison ofsamples rapidly cooled (e.g., deliberately quenched on to a large metalplate) versus samples cooled more slowly (e.g., naturally cooled bypulling from a conventional tube furnace) revealed no discernabledifferences. Accordingly, the possibility of using controlled cooling,particularly through rather low temperatures (e.g., temperature ofperhaps as low as about 250° C., about 200° C., about 150° C., or evenabout 100° C.), may be optionally used to improve resistivity control.

Additionally, or alternatively, it is to be noted that, after a wafer orsubstrate has been subject to the thermal treatment detailed herein, itmay optionally be cooled to a temperature of between greater than about75° C. and less than about 250° C., or between about 100° C. and lessthan about 200° C., and held at this temperature, or within thistemperature range, for some period of time (e.g., a few minutes to aboutan hour, such as about 5 minutes to less than about 60 minutes, or about10 minutes to less than about 45 minutes, or about 15 minutes to lessthan about 30 minutes).

c. Relaxation of Resistivity after Thermal Treatment

It is also to be noted that, in some instances, there is relaxation ofresistivity, which occurs after annealing. For example, the resistivityof a sample, after thermal treatment, may drift at a given temperature,such as room temperature, by amounts of about 10%, about 20%, about 30%,about 40%, or even about 50%, for a for a period of time (e.g., a fewtens of hours, such as about 10 hours, about 25 hours, about 50 hours,about 75 hours, about 100 hours or more, or up to about 5 days or even aweek), before it settles down to its final or substantially stablevalue. Experience to-date suggests sample resistivity, following thethermal treatment detailed herein, actually drifts upward, to highervalues, over time. Sometimes, several days, or even a week, may passbefore the final, or substantially stable, value of resistivity may bedetermined. The measurements described here have included such a roomtemperature stabilization period. It is to be further noted thatexperience to-date suggests resistivity relaxation rates may be enhancedby raising the temperature of the sample slightly above room temperature(e.g., by raising relaxation temperature to greater than about 25° C.and less than about 75° C., or greater than about 40° C. and less than50° C.).

3. Alternative Approach—a Two Step Anneal Process

Some experiments to-date also indicate that it may alternatively beadvantageous to apply a two step anneal in place of the single stepanneal at a properly chosen temperature. The two step process involvesthe addition of a lower temperature pre-anneal step, prior to the highresistivity anneal set forth herein above at whatever temperature thatis determined to be suitable for the wafer, or wafer ensemble, inquestion. In at least some instances, both the time and the processwindow to convert such wafers to the high resistivity state may beimproved with this two step approach; in other words, it may be thatless annealing time in the higher temperature range may be used and/or awider parameter window, in terms of the three coupled parameters, may beachieved.

The purpose of the pre-anneal is to generate a relatively largeconcentration of purely ‘normal’ thermal donors (i.e., at temperaturesless than about 480° C.), in concentrations near to or exceeding theconcentration of boron in the wafer prior to the high resistivityanneal. It may be advantageous to do this at a temperature at whichnormal thermal donors are generated most rapidly. The maximum rates ofthermal donor generation typically occurs at temperatures between about,for example, greater than about 425° C. and less than about 460° C., orabout 435° C. about 450° C.

The amount of time at these temperatures needed to create sufficientlyhigh concentrations of thermal donors will vary with the boron andoxygen concentrations. It may, however, be easily determinedexperimentally by monitoring sample resistivity over time. Theconcentration of thermal donors exceeds that of the boron concentrationwhen the sample converts from p-type to n-type.

Following the installation of a sufficiently high concentration ofnormal thermal donors in the low temperature regime, a highertemperature (e.g., a temperature greater than about 480° C.) anneal(i.e., an appropriate temperature for the oxygen and boron concentrationof the wafers in question) is then applied to these wafers, in order toconvert these wafers to a high resistivity state. Such a two stepembodiment may be employed either after or before metallization, asdescribed elsewhere herein (for the single step embodiment).

In this regard it is to be noted that, in most cases, the total time forsuch a two step process may exceed that of the one step process.Possible advantages of such a treatment, however, may include improvedprocess stability and less time spent at temperatures greater than about480° C.

4. Assemblies and Variability Therein

The process of the present invention enables the preparation of anassembly of CZ silicon structures, or CZ wafers, as set forth herein;that is, the present invention enables an assembly of CZ siliconstructures, or CZ wafers, to be prepared, such that each of thestructures or wafers present therein possesses the high resistivityfeatures of the present invention. Such an assembly may contain, forexample, at least about 10 structures or wafers, and may optionallycontain at least about 20, about 30, about 40, about 50 or morestructures or wafers.

In accordance with the present invention, the oxygen concentration oftwo or more of these wafers, or the substrates of these structures, inthe above-noted assembly may differ by at least about 0.1 ppma, about0.5 ppma, about 1 ppma, about 1.5 ppma, about 2 ppma, about 2.5 ppma,about 3 ppma, about 3.5 ppma, about 4 ppma, about 4.5 ppma, or about 5ppma. Additionally, or alternatively, the oxygen concentration of eachof said wafers or substrates and in the above-noted assembly may bewithin the range of about 5 ppma to about 20 ppma, from about 8 ppma toabout 15 ppma, about 10 to about 14 ppma, or about 11 to about 13 ppma.

Also in accordance with the present invention, the boron concentrationof two or more of these wafers, or the substrates of these structures,in the above-noted assembly may differ by at least about 1%, about 2%,about 3%, about 4%, about 5%, about 6%, about 7%, about 8%, about 9%,about 10%, about 12%, about 14%, about 16%, about 18%, or about 20%.Additionally, or alternatively, the boron concentration of two or moreof said wafers or substrates in said assembly may differ by at leastabout 1% to less than about 20%, from about 2% to about 18%, from about4% to about 16%, from about 6% to about 14%, or from about 8% to about12%.

In this regard it is to be noted that a population of such substrates,or wafers, with a distribution of [Oi] and/or [B] in the population,even a distribution larger than the ranges defined above, may beoptionally measured and sorted into two or more groups designed to besubjected to thermal treatments at different temperatures. In this way,the added cost of tightly controlling wafer, or substrate,specifications may be offset by an added complication of two or moredifferent annealing schedules.

In this regard it is to be still further noted that, with respect tovariability in oxygen concentration and/or boron concentration,variations may also exist within a given wafer or substrate, as well.More specifically, in one embodiment, the present invention is directedto wafer, and/or a process for the preparation thereof, wherein thewafer has a front surface and a back surface, a circumferential edge, acentral axis which is substantially perpendicular to each of said frontand back surfaces, and a radius extending from said central axissubstantially parallel to each of said front and back surfaces andtoward the circumferential edge, said wafer having an oxygenconcentration, and/or a boron concentration, which varies along saidradius. Alternatively, the present invention may be directed to astructure having a single crystal silicon substrate, said substrate ofthe structure having a front stratum and a back stratum, acircumferential edge, a central axis which is substantiallyperpendicular to each of said front and back stratums, and a radiusextending from said central axis substantially parallel to each of saidfront and back stratums and toward the circumferential edge, saidsubstrate having an oxygen concentration, and/or a boron concentration,which varies along said radius. In either of such embodiments, theoxygen concentration along said radius may vary by at least about 0.1ppma, about 0.5 ppma, about 1 ppma, about 1.5 ppma, about 2 ppma, about2.5 ppma, about 3 ppma, about 3.5 ppma, about 4 ppma, about 4.5 ppma, orabout 5 ppma (the concentration for example ranging from about 5 ppma toabout 20 ppma, from about 8 ppma to about 15 ppma, from about 10 toabout 14 ppma, or from about 11 to about 13 ppma). Additionally, oralternatively, the boron concentration along said radius may vary by atleast about 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 14%, 16%, 18%or 20% (the concentration for example ranging from at least about 1% toless than about 20%, from about 2% to about 18%, from about 4% to about16%, from about 6% to about 14%, or from about 8% to about 12%).

5. Other Wafer Embodiments

It is to be noted that wafers subjected to the thermal treatmentdetailed herein may optionally be an epitaxial or a SOI wafer; that is,the wafer subjected to the process of the present invention mayoptionally have an epitaxial layer present on a surface thereof, or itmay be part of a multi-layered structure, wherein the handle waferthereof has high resistivity. Accordingly, in these embodiments, thejoint specification of the three parameters refers to thecharacteristics of the epitaxial substrate, or the substrate below theburied oxide layer of the SOI structure (i.e., the handle wafer of thestructure). The epitaxial or SOI device layer itself may be ofessentially any resistivity. Additionally, the oxygen concentration ofan epitaxial layer may be within conventional ranges known in the art,and thus naturally low.

It is to be further noted that epitaxial deposition may be performed bymeans known in the art. Additionally, the semiconductor-on-insulatorstructure may also be prepared using means known in the art (e.g.,hydrogen-implantation or bonded applications). Thesemiconductor-on-insulator composite may be formed, for example, asdescribed in lyer et al., U.S. Pat. No. 5,494,849.

6. Device Manufacturing

It is to be noted that, although silicon wafers with high resistivitycan be manufactured as described above wherein the boron concentration,oxygen concentration, and annealing temperature are controlled, suchsilicon wafers would still undergo device manufacturing procedures inorder to have a finished high resistivity semiconductor device product.Semiconductor device manufacturing processes subject silicon wafers tothermal heating and cooling, and devices are added to the surface of thesilicon wafers. This heating and cooling normally affect theconcentration and distribution of boron and oxygen, and may reduce theresistivity of silicon wafers wherein high resistivity is obtained bymeans as set forth herein; that is, a high resistivity silicon wafermanufactured by the process set forth herein may lose its highresistivity upon being subjected to a device manufacturing process.Therefore, one aspect of the present invention involves manipulating thedevice manufacturing process so that high resistivity semiconductordevices (i.e., a device typically having a resistivity greater thanabout 1 kohm-cm) can be manufactured for use in electronic devices. Suchdevices include, for example, electronic devices, such as integratedcircuits or microchips, as well as passive electrical devices, such asplanar inductors or RC filters.

Accordingly, in one embodiment, the present invention is directed to amethod for manufacturing a semiconductor device containing a siliconwafer, wherein the annealing temperature, concentration of boron, andconcentration of oxygen are maintained in accordance with therelationship set forth in Equation (1a) provided elsewhere herein,and/or are in accordance with the ranges provided elsewhere herein.

As previously noted, the high resistivity state created by the annealingprocess is typically not stable to high temperature heat treatments.Accordingly, at elevated temperatures the effect may essentially beerased. Therefore, the specific heat treatment that is applied to wafersof a given specification, in order to converts them to the highlyresistive state, is, in at least some embodiments, preferably applied ator near the end of a device manufacturing process. Most preferably, thisheat treatment typically, but not necessarily, acts as theusually-required “post metallization anneal” step of a device makingprocess. However, although the effects of the process of the presentinvention may be lost if the resulting wafer, or silicon structure, issubjected to a subsequent heating step involving a temperature that istoo high, or a duration that is too long, the high resistivity state oreffect can be returned or recovered by reheating the wafer or structure,in a manner consistent with the present invention.

It is to be further noted that a basic embodiment of a devicemanufacturing process, consistent with the present invention, may beillustrated by the block diagram provided in FIG. 12. Alternatively,however, as illustrated by the block diagram in FIG. 13, it may bedesirable to apply the high resistivity annealing treatment prior tometallization. For instance, the final finished device in question maybe unstable to even the minimum temperature needed to achieve thedesired high resistivity state or effect (thought to be, for example,about 480° C.). If so, a post metallization anneal may then beperformed, but it is preferably limited to a temperature not muchgreater than about 400° C. (e.g., about 425° C. or about 450° C.) andfor relatively short periods of time (e.g., up to, for example, amaximum of about 10 to about 40 minutes, or about 20 to about 30minutes), in order to avoid reducing or eliminating the high resistivityeffect. However, it may be possible to extend the parameters of asubsequent post-metalization heat treatment to higher temperaturesand/or longer times, if the wafers have a very low oxygen concentration.

7. Control of Oxygen Precipitation During the Device Process

It is to be noted that the oxygen concentration which is important forthe present invention is the interstitial oxygen concentration after theprocess for making the device. Accordingly, if there is any measurableloss of oxygen to oxygen precipitation, this is to be taken intoaccount. For most applications typically of interest here (e.g., veryhigh speed, and hence very small, devices), the “thermal budgets” forthe processes may be limited. In other words, there may be a limitedscope for oxygen loss to precipitation. Thus, the initial oxygenconcentration may be essentially equal, for all intents and purposes, tothe final oxygen concentration. If this is not the case, then some caremay be exercised to insure uniform oxygen precipitation behavior, whichmay mean, for example, in at least some instances, subjecting the waferor structure to a “tabula rasa” thermal treatment (i.e., a process forno oxygen precipitation, such as that disclosed in U.S. Pat. No.6,336,968, which is incorporated herein by reference), or a MDZ thermaltreatment (i.e., a process for controlling oxygen precipitation, such asthat disclosed in U.S. Pat. Nos. 5,994,761; 6,204,152; 6,191,010;6,284,384 and 6,236,104, which are incorporated herein by reference).

8. Measurement Techniques

In accordance with the present invention, it is to be noted thatreferences to resistivity may refer to the surface resistivity, asmeasured by a surface four point probe using means known in the art,and/or may refer to the resistivity as determined at least about 50,about 75, about 100, about 125, about 150, about 175, about 200 micronsor more below the wafer surface, or substrate stratum, as measured byspreading resistance using means known in the art.

Dopant concentrations may be measured by SIMS, Hall Effect, and/orInfrared Spectroscopic techniques, which are generally known in the art.Thermal donors in silicon may be detected by Hall Effect and/or infraredabsorption spectroscopy, again using means known in the art.

9. CZ Wafer Diameter

It is to be noted that, the CZ wafers prepared in accordance with thepresent invention typically have a nominal diameter of at least about150 mm, and preferably have a nominal diameter of at least about 200 mm,about 300 mm, or more.

10. Exemplary Process Embodiments

In one preferred embodiment of the present invention, a high resistivitywafer, or substrate of a structure, as defined herein above, is formedby subjecting a CZ silicon wafer, or silicon structure comprising a CZwafer as a substrate, which has an interstitial oxygen concentration ofabout 12 to about 15 ppma and a boron concentration of about 2.75×10¹⁴cm⁻³ to about 3.25×10¹⁴ cm⁻³, to a heat-treatment for about 10 to about100 minutes at about 505 to about 515° C. The resistivity of theresulting wafer, or the substrate of the silicon structure, is in therange of about 1200 to about 1900 ohm-cm.

In another preferred embodiment of the present invention, a highresistivity wafer, or substrate of a structure, as defined herein above,is formed by subjecting a CZ silicon wafer, or silicon structurecomprising a CZ wafer as a substrate, which has an interstitial oxygenconcentration of about 12 to about 15 ppma and a boron concentration ofabout 2.75×10¹⁴ cm⁻³ to about 3.25×10¹⁴ cm⁻³, to a heat-treatment forabout 80 to about 150 minutes at about 500 to about 525° C. Theresistivity of the resulting wafer, or the substrate of the siliconstructure, is in the range of about 500 to about 2000 ohm-cm.

In yet another preferred embodiment of the present invention, a highresistivity wafer, or substrate of a structure, as defined herein above,is formed by subjecting a CZ silicon wafer, or silicon structurecomprising a CZ wafer as a substrate, which has an interstitial oxygenconcentration of about 8 to about 12 ppma and a boron concentration ofabout 5.50×10¹³ cm⁻³ to about 6.00×10¹³ cm⁻³, to a heat-treatment forabout 60 to about 80 minutes at about 490 to about 495° C. Theresistivity of the resulting wafer, or the substrate of the siliconstructure, is in the range of about 1500 to about 2800 ohm-cm.

In yet another preferred embodiment of the present invention, a highresistivity wafer, or substrate of a structure, as defined herein above,is formed by subjecting a CZ silicon wafer, or silicon structurecomprising a CZ wafer as a substrate, which has an interstitial oxygenconcentration of about 8 to about 12 ppma and a boron concentration ofabout 5.50×10¹³ cm⁻³ to about 6.00×10¹³ cm⁻³, to a heat-treatment forabout 60 to about 80 minutes at about 490 to about 495° C. Theresistivity of the resulting wafer, or the substrate of the siliconstructure, is in the range of about 1500 to about 2500 ohm-cm.

In yet another preferred embodiment of the present invention, a highresistivity wafer, or substrate of a structure, as defined herein above,is formed by subjecting a CZ silicon wafer, or silicon structurecomprising a CZ wafer as a substrate, which has an interstitial oxygenconcentration of about 6 to about 8 ppma and a boron concentration ofabout 1.75×10¹⁴ cm⁻³ to about 2.25×10¹⁴ cm⁻³, to a heat-treatment forabout 40 to about 110 minutes at about 510 to about 535° C. Theresistivity of the resulting wafer, or the substrate of the siliconstructure, is in the range of about 350 to about 11,000 ohm-cm.

In yet another preferred embodiment of the present invention, a highresistivity wafer, or substrate of a structure, as defined herein above,is formed by subjecting a CZ silicon wafer, or silicon structurecomprising a CZ wafer as a substrate, which has an interstitial oxygenconcentration of about 6 to about 8 ppma and a boron concentration ofabout 4.5×10¹³ cm⁻³ to about 5.0×10¹³ cm⁻³, to a heat-treatment forabout 10 to about 70 minutes at about 495 to about 530° C. Theresistivity of the resulting wafer, or the substrate of the siliconstructure, is in the range of about 800 to about 19,500 ohm-cm.

Additionally, in these or yet other embodiments set forth herein, it isto be noted that the silicon wafer, or the substrate of the siliconstructure, may optionally be doped with something other than gold (Au);that is, in some embodiments of the present invention, the highresistivity wafer, or substrate of the high resistivity siliconstructure, is not gold-doped.

EXAMPLES

The following Examples are presented for illustration purposes only.Accordingly, they are not to be viewed in a limiting sense.

Example 1

An example of the results that may be obtained using the techniques ofthe present invention, and as set forth in Equation (1a) herein, isfound in FIG. 14. The resistivity data in FIG. 14 was obtained from HallEffect determinations of carrier concentrations at different stagesduring the annealing of a wafer under conditions defined in thisinvention. In this example, a sample initially having a resistivity ofabout 300 ohm-cm (i.e., [B] equal to about 4e13 cm⁻³), and an oxygenconcentration of about 6.5e17 cm⁻³, was used. The appropriate annealingtemperature to achieve the high resistivity effect in a sample of thistype was determined to be about 530° C. In this particular example,previously generated thermal donors were also present in the sample andthe sample was actually n-type prior to the annealing (due to a prior 3hour annealing at about 450° C.).

FIG. 14 shows the development of the resistivity, as deduced from theHall Effect measurements, of this sample over time during annealing atabout 530° C. The initial n-type sample relaxes quickly toward a veryhigh value of resistivity. This high value of resistivity (2-20 kohm-cm)is persistent for about two hours of annealing. This is a rathersurprising result, and different to that expected from “normal” thermaldonors. Furthermore, measurements taken at different locations (e.g.,radial locations) within the wafer, and even with other wafers of asimilar type, showed a similar behavior. Similar behavior has beenobserved in many samples over a wide range of appropriate parametercombinations, and more examples are provided herein below.

It is to be noted that spreading resistance measurements throughout thedepth of such samples show that the bulk resistivity is very uniform.This is also very different to the behavior of conventional thermaldonors. In the case of conventional thermal donors, when near thetransition from p-type to n-type material, the natural variation ofoxygen concentrations due to striations (e.g., with typical periods ofabout 100 microns) in its incorporation during growth are enough tocause the wafer to vary throughout the wafer thickness, even flippingfrom n-type to p-type throughout the thickness, in sync with the oxygenstriations. Notably, high resistivity material produced by the techniqueof the present invention appears to be unaffected by oxygen (or boron)concentration striations.

Example 2

Further to Example 1, above, and to demonstrate further the highlydesirable “approximate” matching of conditions afforded by the presentinvention (and in accordance with Equation (1a) presented herein),samples similar to that used in Example 1 were annealed at temperaturesnear the calculated temperature of, in this instance, about 530° C. forthis type of material. The results of the saturated resistivityfollowing the anneal are shown in FIG. 15.

Example 3 Comparative Example

This Example is to illustrate how the resistivity versus temperaturecurve, ρ(T), would look without a self-compensation effect.

In a simple “normal” case, when there is no reconstruction-basedself-compensation, the resistivity is controlled essentially only by theachieved difference N=2N_(td)(T,C)−N_(A). At N>0, the carrier (electron)concentration is n=N. At N<0, the carrier (hole) concentration is p=−N.More generally, at a very small difference N, the resistivity mayapproach the intrinsic value, and a more general expression for n and pmay be used in this case (which is seldom to be met):n=N/2+[(N/2)² +n _(i) ²]^(1/2),  (2)p=−N/2+[(N/2)² +n _(i) ²]^(1/2),  (3)where n_(i) is the intrinsic electron concentration (close to about1.3×10¹⁰ cm⁻³ at room temperature). The resistivity isρ=1/(eμ_(n)n+eμ_(p)p). The drift mobilities μ_(n) and μ_(p) are about1,550 cm²/sV and about 450 cm²/sV, respectively (at room temperature).

The donor/acceptor difference, N, is convenient to write using thetemperature T_(c) of the required (in absence of the newly discovered“self-compensation” effect) precise coincidence of N_(A) and 2N_(td):N=N _(A)[exp(E _(td) /kT−E _(td) /kT _(c))−1].  (4)Thus, quantity is almost a universal function of the temperaturedeviation T−T_(c), since the parameter E_(td)/kT_(c) ² does notsubstantially change within a narrow range of T_(c).

The calculated dependence of the achieved resistivity, in dependence ofthe temperature deviation from the temperature T_(c) of precisecompensation, is shown in FIG. 15 a. For a boron concentration N_(A),typical values were assumed: about 3×10¹³ cm⁻³ (which correspond to thestarting resistivity ρ_(A) equal to about 463 ohm-cm) and about 10¹⁴cm⁻³ (resistivity is about 139 ohm-cm). The compensation temperatureT_(c) was taken to be about 520° C. It is to be noted here that theresult is almost insensitive to T_(c). The plot of FIGS. 15 a and 15 bgives an impression of the absolute value of achieved resistivity.However, the achieved carrier concentration is actually scaled by N_(A),according to Equation (4), above, and the resistivity is accordinglyscaled by the initial value ρ_(A). Therefore, there is a resistivityenhancement factor F_(r) (the ratio of the achieved resistivity to theinitial resistivity) that is independent of the initial resistivity andsensitive only to the temperature deviation T−T_(c). The enhancementfactor is plotted in FIG. 15 b.

Examples 4-9

Additional data was collected from examining many examples of creatingthe high resistivity state from a variety of boron and oxygenconcentration combinations, using the techniques and relationshipsoutlined herein (see, e.g., Equation (1a)). Provided below are some datacharts showing results of experiments in which an “ideal” or preferredanneal temperature was calculated for the given [Oi] and [B] of thewafer in question (in accordance with Equation (1a)). Samples were takenfrom this wafer and then annealed at a temperature near this temperaturefor a variety of times. Other samples were annealed at othertemperatures in the vicinity of the “ideal” or preferred temperature fora variety of times. In this way further data regarding the window size,or range of acceptable variations, was obtained. It is to be noted thatsome of the samples were given a pre-anneal at 450° C., in order togenerate a high concentration of “stable” or normal thermal donors priorto the self-compensation anneal at the calculated temperature.

Examples of the increase of resistivity achieved by applying thistechnique are given below. In these examples, wafers of variouscombinations of oxygen and boron concentration were collected. Theactual oxygen and boron concentration at the center position of eachwafer in the test is shown in the heading to each individual data chart(i.e., Tables 1-6). Using the technique described above, an annealingtemperature appropriate to the particular combination of oxygen andboron concentration was determined. This calculated temperature is alsolisted in the heading to each chart. The wafers were then cut into smallpieces and each piece was given an individual anneal at a temperature ator near the calculated temperature for the wafer it came from forcertain periods of time. The time evolution of sample resistivity duringannealing in a temperature range around the ideal calculated temperaturewas determined by four point probe measurements following the anneal(some period of room temperature storage—on the order of at least a fewdays—was allowed to happen between the anneal and the four point probemeasurements—see below).

The resistivity results obtained are indicated in the box appropriate tothe annealing time and temperature. In each of the sample boxes, anindication of whether the sample was determined to be n-type or p-typeis also provided. However, it is to be noted that, at very high valuesof resistivity (e.g., greater than about 1 kohm-cm), the determinationof type may be somewhat questionable using the method employed here.

By investigating a wide range of boron and oxygen concentrationcombinations, the general principle of the present invention wasconfirmed. A rather wide variety of calculated “ideal” or preferredtemperatures are covered here (from about 495° C. to about 530° C.) withthis sample collection. In general, the agreement with the model is goodand the window in temperature found is uniformly large.

Example 4

TABLE 1 Resistivity (in ohm-cm) of samples from wafer 04246959, with apre-anneal at about 450° C. for three hours; Initial resistivity wasabout 43 ohm-cm; [B] was about 3.03 × 10¹⁴ cm⁻³; [Oi] was about 14 ppma(7 × 10¹⁷ cm⁻³); and T_(calc) was about 510° C. Time 505° C. 510° C.515° C. 10 min 1848 1860 1600 N-, p- n- n- 20 min 1705 1613 1599 n-, p-n- n- 30 min 1543 1207 n-, p- n- 40 min 1770 303 1640 n-, p- p- n- 50min 1774 1866 n- n- 60 min 1716 1305 1387 n-, p- n- n- 70 min 1302 18771383 n-, p- p- p- 80 min 1314 1531 p- n- 90 min 1347 p- 100 min  1565 p-In this regard it is to be noted that resistivities reported here andelsewhere herein may be easily converted to [B] using calculations knownin the art. (See also conversion calculator available online at, forexample, www.solecon.com (i.e., www.solecon.com/sra/rho2ccal.htm).

Example 5

TABLE 2 Wafer 04246959 (without pre-anneal); Initial resistivity about43 ohm-cm; [B] about 3.03 × 10¹⁴ cm⁻³; [Oi] about 7 × 10¹⁷ cm⁻³;T_(calc) about 510.4° C. Time 505° C. 510° C. 515° C. 520° C. 525° C.530° C. 535° C.  30 61.4 min p-  40 86.2 63 52.4 min p- p- p-  50 85  9373.8 77.4 54.1 min p- p- p- p- p-  60 109 132.5  153 75.4 81.5 56.3 minp- n-, p- p- p- p- p-  70 238 153  120 53.8 min p- p- p- p-  80 2003 449 635 141 86.1 66.6 min n- p- p- p- p- p-  90 1733 1450 1000* 139 103 70min n-, p- n-, p- p- p- p- p- 100 190 942  726* 86.6 275 65.3 min n- p-p- p- p- p- 110 48 1631  107* 1445 min n- n-, p- n- p- 120 1359  26.9*80.4 80.1 min p- n- n-, p- p- 130 1810  490* 143 min p- n- p- 150 250 508* min n- p-

Example 6

TABLE 3 Wafer 419DFA-1 (without pre-anneal); Initial resistivity about225 ohm-cm; [B] about 5.77 × 10¹³ cm⁻³; [Oi] about 9.28 ppma; T_(calc)about 494.6° C. 485° 490° 495° 500° 505° 510° 515° 520° Time C. C. C. C.C. C. C. C.  20 min  496  275 p- p-  40 min  752  476 p- p-  60 min 27751497 231  262 286 p- p- p- p- p-  70 min 2310 1978 450  352 219 p- p- p-p- p-  80 min 2106 263  315 188 p- p- p- p-  90 min 274  419 258 p- p-p- 100 min 293  374 205 p- p- p- 110 min 392  383 211 p- p- p- 120 min437  560 p- p- 180 min  423 p- 240 min 1359 p-

Example 7

TABLE 4 Wafer 419DFA-2 (without pre-anneal); Initial resistivity about227 ohm-cm; [B] about 5.72 × 10¹³ cm⁻³; [Oi] about 9.41 ppma; T_(calc)about 495.8° C. 485° 490° 495° 500° 505° 510° 515° 520° Time C. C. C. C.C. C. C. C.  20 min  268  402 p- p-  40 min  588  673 p- p-  60 min 24441732 259  322 409 p- p- p- p- p-  70 min 2472 1984 296  447 281 p- p- p-p- p-  80 min 1556 275  375 195 p- p- p- p-  90 min 284  354 288 p- p-p- 100 min 450  360 205 p- p- p- 110 min 310  379 222 p- p- p- 120 min469  807 p- p- 180 min  349 = p- 3 h 240 min 1793 = p- 4 h

Example 8

TABLE 5 Wafer MQ0AMMH (without pre-anneal); Initial resistivity about 65ohm-cm; [B] about 2.00 × 10¹⁴ cm⁻³; [Oi] about 7.24 × 10¹⁷ cm⁻³;T_(calc) about 519.1° C. Time 500° C. 505° C. 510° C. 515° C. 520° C.525° C. 530° C. 535° C.  10 min 96.8 81.2 82.5 84.1 p- p- p- p-  20 min172.6 124  137 92.9 p- p- p- p-  30 min 236 239  142 294 192 n-, p- p-p- p- p-  40 min 385 1015  193 290 160 122 n-, p- n- p- p- p- p-  50 min174 87 1980 4300 175 127.6 n- n- p- p- p- p-  60 min 44 50 2050 11000132.5 n- n- p- n-, p- p-  70 min 40 55.5  720* 658 129 n- n- p- p- p- 80 min 25.7 23.4  940* 217 312 186 n- n- n- n- p- p-  90 min 15.8 25.5 52.6 93 3630 408 n- n- n- n- p- p- 100 min  162 344 3260 n- p- p- 110min  125 23.8 419 n- n- p-

Example 9

TABLE 6 Wafer TR6 (CTSQX003) (without pre-anneal); Initial resistivityabout 270 ohm-cm; [B] about 4.81 × 10¹³ cm⁻³; [Oi] about 6.6 × 10¹⁷cm⁻³; T_(calc about 531.3° C.) Time 495° C. 500° C. 505° C. 510° C. 515°C. 520° C. 525° C. 530° C. 535° C. 10 min 1010 1035 970 2400 830  490*p- p- p- p- p- p- 20 min 1254 19500 2020 n- n- p- 30 min 293 5070 2400*n- p- p- 40 min 93.9 786 8600 n- n- p- 50 min 99.6 178 7800 n- n- p- 60min 46.5 188 7050 n- n- p- 70 min 56.9 379  800 n- n- p- 80 min 35.5 64 433 n- n- n- 90 min 22.4 74.3  219 n- n- n-

Example 10

In this Example the effect of short post-process anneals at about 400°C. on the stability of the high resistivity state was also investigated.Two samples were used in these tests. They were samples made highlyresistive by the present process. This was achieved by annealing atabout 530° C. (the samples used in this test were similar to the onewhose resistivity results were illustrated in FIG. 14: in other words,an initial boron controlled resistivity of about 300 ohm-cm and anoxygen concentration of about 6.6e17 cm⁻³). Following the annealingtreatment to create the highly resistive state with this material, oneof the samples was p-type and the other n-type. Both were highlyresistive, with resistivities in excess of about 1 kohm-cm.

Of interest in this experiment was the stability of the highly resistivestate created by the annealing process described here to a further heattreatment. To this end, these samples were subjected to sequentialannealing at about 400° C., with the resistivity determined betweenanneals. The time dependence of the resistivity and the relaxation ofthe highly resistive state during such anneals was thus determined overannealing times between about 10 and about 60 minutes. These results aresummarized in FIG. 17.

At time equals 0 minutes, the initial value of the high resistivity ofthe wafers in the test is given. After the shortest anneal (i.e., about10 minutes) the resistivity still remains high. For initially p-typesample, it is even increased (and the conductivity type is changed ton-type). Further increasing the annealing time led to a gradualreduction in the resistivity. Finally, after about 60 minutes, theresulting samples had a relatively low resistivity, comparable to thatof the as-grown material (e.g., about 300 ohm-cm). The conclusion drawnhere is that the high resistivity state is preserved after treatments atabout 400° C., providing the anneal is not too long (e.g., less thanabout 60 minutes). For samples CTS-QX003 and 18HLBA-1A, with a moderateboron concentration, a high resistivity was achieved by annealing atabout 530° C. The curves in FIG. 17 are for the two different sample, ofthe opposite achieved conductivity type.

Example 11

In this Example, the effect of an oxygen denuded zone on the on thecreation of a high resistivity substrate was examined; that is, theimpact of an oxygen out-diffused surface region on the conversion to ahigh resistivity state was investigated. In this experiment, largeamounts of oxygen was out-diffused from a sample containing about 6.6e17cm⁻³ bulk oxygen by a thermal treatment at about 1100° C. for about 3hours. The characteristic diffusion length of 2(Dt)^(1/2) for thistreatment is about 17 microns. The wafer resistivity was about 300ohm-cm and the desired anneal temperature resulting from this particularcombination of oxygen and boron concentrations was determined to beabout 530° C.

Samples were annealed with and without the oxygen out-diffusiontreatment, and also with and without a 450° C., 3 hour thermal donorpre-anneal inserted between the out diffusion and the high resistivitytreatment. A sample description is show below:

300 mm quarters for resistivity variation tests Quarter Oi (ppma) RQscratch Center Atmosphere TT 6800 A 12.772 N2 + O2 1100° C. 3 h + 40 min530° C. B 12.772 N2 + O2 1100° C. 3 h + 3 h 450° C. + 40 min 530° C. C12.772 N2 + O2 40 min 530° C. D 12.772 N2 + O2 3 h 450° C. + 40 min 530°C.The results of spreading resistance profiling of the samples followingthe anneal are shown in the FIGS. 17 A-D.

Examples 12-17

Additional experiments were conducted similar to those detailed inExamples 4-9, above. The details of these experiments (i.e., Examples12-17) are summarized below:

Example 12

Multiple CZ wafers, or silicon structures comprising a substrate derivedfrom a CZ silicon structure, having interstitial oxygen concentrationsof about 12 to about 15 ppma and boron concentrations of about 2.75×10¹⁴cm⁻³ to about 3.25×10¹⁴ cm⁻³, were heat treated for about 10 to about100 minutes at about 505 to about 515° C. The resulting wafers, orsubstrates of said structures, had a resistivity in the range of about1200 to about 1900 ohm-cm.

Example 13

Multiple CZ wafers, or silicon structures comprising a substrate derivedfrom a CZ silicon structure, having interstitial oxygen concentrationsof about 12 to about 15 ppma and boron concentrations of about 2.75×10¹⁴cm⁻³ to about 3.25×10¹⁴ cm⁻³, were heat treated for about 80 to about150 minutes at about 500 to about 525° C. The resulting wafers, orsubstrates of said structures, had a resistivity in the range of about500 to about 2000 ohm-cm.

Example 14

Multiple CZ wafers, or silicon structures comprising a substrate derivedfrom a CZ silicon structure, having interstitial oxygen concentrationsof about 8 to about 12 ppma and boron concentrations of about 5.50×10¹³cm⁻³ to about 6.00×10¹³ cm⁻³, were heat treated for about 60 to about 80minutes at about 490 to about 495° C. The resulting wafers, orsubstrates of said structures, had a resistivity in the range of about1500 to about 2800 ohm-cm.

Example 15

Multiple CZ wafers, or silicon structures comprising a substrate derivedfrom a CZ silicon structure, having interstitial oxygen concentrationsof about 8 to about 12 ppma and boron concentrations of about 5.50×10¹³cm⁻³ to about 6.00×10¹³ cm⁻³, were heat treated for about 60 to about 80minutes at about 490 to about 495° C. The resulting wafers, orsubstrates of said structures, had a resistivity in the range of about1500 to about 2500 ohm-cm.

Example 16

Multiple CZ wafers, or silicon structures comprising a substrate derivedfrom a CZ silicon structure, having interstitial oxygen concentrationsof about 6 to about 8 ppma and boron concentrations of about 1.75×10¹⁴cm⁻³ to about 2.25×10¹⁴ cm⁻³, were heat treated for about 40 to about110 minutes at about 510 to about 535° C. The resulting wafers, orsubstrates of said structures, had a resistivity in the range of about350 to about 11,000 ohm-cm.

Example 17

Multiple CZ wafers, or silicon structures comprising a substrate derivedfrom a CZ silicon structure, having interstitial oxygen concentrationsof about 6 to about 8 ppma and boron concentrations of about 4.5×10¹³cm⁻³ to about 5.0×10¹³ cm⁻³, were heat treated for about 10 to about 70minutes at about 495 to about 530° C. The resulting wafers, orsubstrates of said structures, had a resistivity in the range of about800 to about 19,500 ohm-cm.

Example 18

In this Example, two groups of CZ wafers were subjected to a highresistivity heat treatment, in accordance with the present invention, inorder to illustrate the behavior of groups of wafers. All wafers in thistest were first subjected to a 3 hour heat treatment at 450° C.Subsequently, the first group of wafers (Group 1) was annealed togetherat a temperature established in accordance with Equation (1a) based ontheir oxygen and boron concentrations (i.e., 530° C. for 30 minutes).The second group of wafers (Group 2) was also annealed together, andalso at a temperature established in accordance with Equation (1a) basedon their oxygen and boron concentrations (i.e., 510° C. for 30 minutes).The results of this Example are summarized in the Table, below:

Resistivity, Thickness Initial (ohm- Resistivity, Group/Wafer (μm) [Oi](ppma) cm) Final (ohm-cm) 1/A 676.5 15.442 105.9 5484.0 1/B 676.5 15.84297.0 18904.0 1/C 672.5 15.535 105.8 8026.8 2/A 714.4 10.970 184.1 4667.02/B 719.0 10.885 188.8 2383.0 2/C 719.2 11.041 184.6 2752.4 2/C 716.310.887 182.8 1330.8

It is to be understood that the above description is intended to beillustrative and not restrictive. Many embodiments will be apparent tothose of skill in the art upon reading the above description. The scopeof the invention should therefore be determined not with reference tothe above description alone, but should be determined with reference tothe claims and the full scope of equivalents to which such claims areentitled.

When introducing elements of the present invention or an embodimentthereof, the articles “a”, “an”, “the” and “said” are intended to meanthat there are one or more of the elements. The terms “comprising”,“including” and “having” are intended to be inclusive and mean thatthere may be additional elements other than the listed elements.

The recitation of numerical ranges by endpoints includes all numberssubsumed within that range. For example, a range described as beingbetween 1 and 5 includes 1, 1.6, 2, 2.8, 3, 3.2, 4, 4.75, and 5.

1. A process for preparing a high resistivity silicon structure, theprocess comprising: subjecting a silicon structure, which comprises a CZsingle crystal silicon substrate having an initial resistivity of atleast about 50 ohm-cm, to a heat-treatment for a duration and at atemperature such that the resulting substrate of the heat-treatedstructure has a concentration of thermal donors [TD] and acceptors [A]wherein the ratio [TD]:[A] is between about 0.8:1 and about 1.2:1. 2.The process of claim 1 wherein said ratio is between about 0.9:1 and1.1:1.
 3. The process of claim 1 wherein the resulting resistivity ofthe heat-treated substrate is at least about 10 times greater than theresistivity as calculated based on the acceptor concentration therein.4. The process of claim 1 wherein the substrate of the silicon structurehas an oxygen concentration ranging from about at least about 5 to lessthan about 20 ppma.
 5. The process of claim 1 wherein the substrate ofthe silicon structure has an initial resistivity ranging from at leastabout 100 to less than about 300 ohm-cm.
 6. The process of claim 1wherein after the heat-treatment the resulting substrate of theheat-treated silicon structure has a resistivity of at least about 1000ohm-cm.
 7. The process of claim 1 wherein boron atoms are the acceptorand oxygen clusters are the thermal donors.
 8. The process of claim 7wherein the boron concentration [B] and the oxygen concentration [Oi] ofthe substrate of the structure, and the temperature, T, of theheat-treatment, are related by the following equation:[B]=1e14([O _(i) ]/[O _(i)]_(ref))^(n)exp(E/kT−E/kT _(ref)) wherein: [B]is the boron concentration; [Oi]_(ref) is the reference interstitialoxygen concentration and is about 6.6e17 cm⁻³; [Oi] is the actualinterstitial oxygen concentration of the substrate of the structure; nis the oxygen exponent and is about 7; E is the activation energy and isabout 4 eV; k is the Boltzmann constant; T is the actual temperature ofthe heat-treatment; and, T_(ref) is the reference temperature and isabout 520° C., and further wherein: (i) for a given boron concentration,[B], the oxygen concentration may be about +/−0.5 ppma of the calculatedconcentration and the temperature of the heat-treatment may be about+/−10° C. of the calculated temperature; (ii) for a given oxygenconcentration, [Oi], the boron concentration may be about +/−20% of thecalculated concentration and the temperature of the heat-treatment maybe about +/−10° C. of the calculated temperature; and, (iii) for a giventemperature of the heat-treatment, T, the oxygen concentration may beabout +/−0.5 ppma of the calculated concentration and the boronconcentration may be about +/−20% of the calculated concentration. 9.The process of claim 1 wherein the substrate of the structure has afront stratum and a back stratum, a circumferential edge, a central axiswhich is substantially perpendicular to each of said front and backstratums, and a radius extending from said central axis substantiallyparallel to each of said front and back stratums and toward thecircumferential edge, said substrate having an oxygen concentrationwhich varies along said radius.
 10. The process of claim 9 wherein saidoxygen concentration along said radius varies from about 5 ppma to about20 ppma.
 11. The process of claim 1 wherein the substrate of thestructure has a front stratum and a back stratum, a circumferentialedge, a central axis which is substantially perpendicular to each ofsaid front and back stratums, and a radius extending from said centralaxis substantially parallel to each of said front and back stratums andtoward the circumferential edge, said substrate having a boronconcentration which varies along said radius.
 12. The process of claim11 wherein said boron concentration along said radius varies from atleast about 1% to less than about 20%.
 13. The process of claim 1wherein the temperature of said heat-treatment is in the range ofgreater than about 480 to less than about 600° C.
 14. The process ofclaim 13 wherein said heat-treatment is for a time of about 10 to about250 minutes.
 15. A process for preparing a high resistivity CZ singlecrystal silicon wafer, the process comprising: subjecting a CZ singlecrystal silicon wafer having a nominal diameter of at least 150 mm andan initial resistivity of at least about 50 ohm-cm to a heat-treatmentfor a duration and at a temperature such that the resulting heat-treatedwafer has a concentration of thermal donors [TD] and acceptors [A]wherein the ratio [TD]:[A] is between about 0.8:1 and about 1.2:1. 16.The process of claim 15 wherein said ratio is between about 0.9:1 and1.1:1.
 17. The process of claim 15 wherein the resulting resistivity ofthe heat-treated wafer is at least about 10 times greater than theresistivity as calculated based on the acceptor concentration therein.18. The process of claim 15 wherein said wafer has an oxygenconcentration ranging from about at least about 5 to less than about 20ppma.
 19. The process of claim 15 wherein said wafer has an initialresistivity ranging from at least about 100 to less than about 300ohm-cm.
 20. The process of claim 15 wherein said wafer has a resistivityafter said heat-treatment of at least about 1000 ohm-cm.
 21. The processof claim 15 wherein boron atoms are the acceptor and oxygen clusters arethe thermal donors.
 22. The process of claim 21 wherein the boronconcentration [B] and the oxygen concentration [Oi] of the wafer, andthe temperature, T, of the heat-treatment, are related by the followingequation:[B]=1e14([O _(i) ]/[O _(i)]_(ref))^(n)exp(E/kT−E/kT _(ref)) wherein: [B]is the boron concentration; [Oi]_(ref) is the reference interstitialoxygen concentration and is about 6.6e17 cm⁻³; [Oi] is the actualinterstitial oxygen concentration of the wafer; n is the oxygen exponentand is about 7; E is the activation energy and is about 4 eV; k is theBoltzmann constant; T is the actual temperature of the heat-treatment;and, T_(ref) is the reference temperature and is about 520° C., andfurther wherein: (i) for a given boron concentration, [B], the oxygenconcentration may be about +/−0.5 ppma of the calculated concentrationand the temperature of the heat-treatment may be about +/−10° C. of thecalculated temperature; (ii) for a given oxygen concentration, [Oi], theboron concentration may be about +/−20% of the calculated concentrationand the temperature of the heat-treatment may be about +/−10° C. of thecalculated temperature; and, (iii) for a given temperature of theheat-treatment, T, the oxygen concentration may be about +/−0.5 ppma ofthe calculated concentration and the boron concentration may be about+/−20% of the calculated concentration.
 23. The process of claim 15wherein the wafer has a front surface and a back surface, acircumferential edge, a central axis which is substantiallyperpendicular to each of said front and back surfaces, and a radiusextending from said central axis substantially parallel to each of saidfront and back surfaces and toward the circumferential edge, said waferhaving an oxygen concentration which varies along said radius.
 24. Theprocess of claim 23 wherein said oxygen concentration along said radiusvaries from about 5 ppma to about 20 ppma.
 25. The process of claim 15wherein the wafer has a front surface and a back surface, acircumferential edge, a central axis which is substantiallyperpendicular to each of said front and back surfaces, and a radiusextending from said central axis substantially parallel to each of saidfront and back surfaces and toward the circumferential edge, said waferhaving a boron concentration which varies along said radius.
 26. Theprocess of claim 25 wherein said boron concentration along said radiusvaries from at least about 1% to less than about 20%.
 27. The process ofclaim 15 wherein the temperature of said heat-treatment is in the rangeof greater than about 480 to less than about 600° C.
 28. The process ofclaim 27 wherein said heat-treatment for a time of about 10 to about 250minutes.
 29. A high resistivity silicon structure comprising a CZ singlecrystal silicon substrate, said substrate having an oxygen concentrationbetween at least about 5 ppma and about 20 ppma, and a concentration ofthermal donors [TD] and acceptors [A] wherein the ratio [TD]:[A] isbetween about 0.8:1 and about 1.2:1.
 30. The structure of claim 29wherein said ratio is between about 0.9:1 and 1.1:1.
 31. The structureof claim 29 wherein said structure is an electronic device.
 32. Thestructure of claim 29 wherein said structure is passive electricaldevice.
 33. The structure of claim 29 wherein the substrate of saidstructure is not Au-doped.
 34. The structure of claim 29 wherein thesubstrate of said structure has a resistivity of at least about 1000ohm-cm.
 35. The structure of claim 29 wherein said structure furthercomprises an epitaxial layer deposited on a surface of said substrate.36. The structure of claim 29 wherein said structure is a silicon oninsulator structure, said structure further comprising an oxide layer ona surface of said substrate, and a device layer on said oxide layer. 37.The structure of claim 29 wherein boron atoms are the acceptor andwherein oxygen clusters are the thermal donors.
 38. The structure ofclaim 37 wherein the resistivity is substantially greater than theresistivity as calculated based on said boron concentration.
 39. Thestructure of claim 38 wherein the resistivity is at least about 10 timesgreater than the resistivity as calculated based on the boronconcentration.
 40. The structure of claim 29 wherein the substrate ofthe structure has a front stratum and a back stratum, a circumferentialedge, a central axis which is substantially perpendicular to each ofsaid front and back stratums, and a radius extending from said centralaxis substantially parallel to each of said front and back stratums andtoward the circumferential edge, said substrate having an oxygenconcentration and/or a boron concentration which varies along saidradius.
 41. The structure of claim 40 wherein said boron concentrationalong said radius varies from at least about 1% to less than about 20%.42. The structure of claim 40 wherein said oxygen concentration alongsaid radius varies from at least about 5 ppma to less than about 20ppma.
 43. A high resistivity CZ single crystal silicon wafer, the waferhaving a nominal diameter of at least 150 mm and an oxygen concentrationbetween at least about 5 ppma and about 20 ppma, and comprising aconcentration of thermal donors [TD] and acceptors [A], wherein theratio [TD]:[A] is between about 0.8:1 and about 1.2:1.
 44. The wafer ofclaim 43 wherein said ratio is between about 0.9:1 and 1.1:1.
 45. Thewafer of claim 43 wherein said wafer is not Au-doped.
 46. The wafer ofclaim 43 wherein said wafer has a resistivity of at least about 1000ohm-cm.
 47. The wafer of claim 43 wherein said wafer further comprisesan epitaxial layer deposited on a surface of said wafer.
 48. Asilicon-on-insulator structure comprising the wafer of claim 43 as thehandle wafer thereof, said handle wafer having an oxide layer on asurface thereof, and a device layer on a surface of the oxide layer. 49.The wafer of claim 43 wherein boron atoms are the acceptor and whereinoxygen clusters are the thermal donors.
 50. The wafer of claim 49wherein the resistivity is substantially greater than the resistivity ascalculated based on said boron concentration.
 51. The wafer of claim 50wherein the resistivity is at least about 10 times greater than theresistivity as calculated based on the boron concentration.
 52. Thewafer of claim 43 wherein the wafer has a front surface and a backsurface, a circumferential edge, a central axis which is substantiallyperpendicular to each of said front and back surfaces, and a radiusextending from said central axis substantially parallel to each of saidfront and back surfaces and toward the circumferential edge, said waferhaving an oxygen concentration and/or a boron concentration which variesalong said radius.
 53. The wafer of claim 52 wherein said boronconcentration along said radius varies from at least about 1% to lessthan about 20%.
 54. The wafer of claim 52 wherein said oxygenconcentration along said radius varies from at least about 5 ppma toless than about 20 ppma.